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<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value"></a><a class="link" href="assign_to_attribute_from_value.html" title="Store an Attribute Value after a Parser Produced a Value (Qi)">Store
          an Attribute Value after a Parser Produced a Value (Qi)</a>
</h5></div></div></div>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h0"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.assign_to_attribute_from_value"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.assign_to_attribute_from_value">assign_to_attribute_from_value</a>
          </h6>
<p>
            The template <code class="computeroutput"><span class="identifier">assign_to_attribute_from_value</span></code>
            is a type used as an attribute customization point. It is invoked by
            all primitive <span class="emphasis"><em>Qi</em></span> parsers in order to store a parsed
            attribute value into the attribute instance provided by the user, if
            this attribute is not a container type (<code class="computeroutput"><span class="identifier">is_container</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
            evaluates to <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>, where <code class="computeroutput"><span class="identifier">T</span></code>
            is the attribute type).
          </p>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h1"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.module_headers"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.module_headers">Module
            Headers</a>
          </h6>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">home</span><span class="special">/</span><span class="identifier">qi</span><span class="special">/</span><span class="identifier">detail</span><span class="special">/</span><span class="identifier">assign_to</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
            Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
          </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              This header file does not need to be included directly by any user
              program as it is normally included by other Spirit header files relying
              on its content.
            </p></td></tr>
</table></div>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h2"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.namespace"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.namespace">Namespace</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
                    <p>
                      Name
                    </p>
                  </th></tr></thead>
<tbody><tr><td>
                    <p>
                      <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span></code>
                    </p>
                  </td></tr></tbody>
</table></div>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h3"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.synopsis"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.synopsis">Synopsis</a>
          </h6>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Attrib</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">assign_to_attribute_from_value</span>
<span class="special">{</span>
    <span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">call</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">val</span><span class="special">,</span> <span class="identifier">Attrib</span><span class="special">&amp;</span> <span class="identifier">attr</span><span class="special">);</span>
<span class="special">};</span>
</pre>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h4"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.template_parameters"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.template_parameters">Template
            parameters</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Parameter
                    </p>
                  </th>
<th>
                    <p>
                      Description
                    </p>
                  </th>
<th>
                    <p>
                      Default
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Attrib</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The type, <code class="computeroutput"><span class="identifier">Attrib</span></code>
                      is the type of the attribute as passed in by the user. This
                      type is not a container type (<code class="computeroutput"><span class="identifier">is_container</span><span class="special">&lt;</span><span class="identifier">Attrib</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                      evaluates to <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>).
                    </p>
                  </td>
<td>
                    <p>
                      none
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">T</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The type, <code class="computeroutput"><span class="identifier">T</span></code>
                      is the type of the attribute instance as produced by the parser.
                    </p>
                  </td>
<td>
                    <p>
                      none
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Enable</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Helper template parameter usable to selectively enable or disable
                      certain specializations of <code class="computeroutput"><span class="identifier">assign_to_attribute_from_value</span></code>
                      utilizing SFINAE (i.e. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_if</span></code>
                      or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">disable_if</span></code>).
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="keyword">void</span></code>
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">Attrib</span></code></span></dt>
<dd><p>
                  A type to be used as the target to store the attribute value in.
                  This type is guaranteed not to be a container type (<code class="computeroutput"><span class="identifier">is_container</span><span class="special">&lt;</span><span class="identifier">Attrib</span><span class="special">&gt;::</span><span class="identifier">type</span></code> evaluates to <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>).
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt>
<dd><p>
                  An attribute instance of type <code class="computeroutput"><span class="identifier">Attrib</span></code>.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">T</span></code></span></dt>
<dd><p>
                  A type as produced by the parser. The parser temporarily stores
                  its parsed values using this type.
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">t</span></code></span></dt>
<dd><p>
                  An attribute instance of type <code class="computeroutput"><span class="identifier">T</span></code>.
                </p></dd>
</dl>
</div>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h5"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.expression_semantics"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.expression_semantics">Expression
            Semantics</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody><tr>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">assign_to_attribute_from_value</span><span class="special">&lt;</span><span class="identifier">Attrib</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">call</span><span class="special">(</span><span class="identifier">t</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">)</span></pre>
<p>
                    </p>
                  </td>
<td>
                    <p>
                      Copy (assign) the value <code class="computeroutput"><span class="identifier">t</span></code>
                      to the attribute <code class="computeroutput"><span class="identifier">attr</span></code>.
                    </p>
                  </td>
</tr></tbody>
</table></div>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h6"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.predefined_specializations"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.predefined_specializations">Predefined
            Specializations</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Template Parameters
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Attrib</span></code>, <code class="computeroutput"><span class="identifier">T</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Assign the argument <code class="computeroutput"><span class="identifier">t</span></code>
                      to <code class="computeroutput"><span class="identifier">attr</span></code>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">unused_type</span></code>,
                      <code class="computeroutput"><span class="identifier">T</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Do nothing.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.h7"></a>
            <span class="phrase"><a name="spirit.advanced.customize.assign_to.assign_to_attribute_from_value.when_to_implement"></a></span><a class="link" href="assign_to_attribute_from_value.html#spirit.advanced.customize.assign_to.assign_to_attribute_from_value.when_to_implement">When
            to implement</a>
          </h6>
<p>
            The customization point <code class="computeroutput"><span class="identifier">assign_to_attribute_from_value</span></code>
            needs to be implemented for a specific type whenever the default implementation
            as shown above is not applicable. Examples for this could be that the
            type <code class="computeroutput"><span class="identifier">Attrib</span></code> is not copy
            constructible.
          </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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